[jhein]

I'm far from an expert but, I do have a mechanical pump and a Quadrajet. No other external check valve other than what the pump (and qjet filter??) may have. After running the motor, it can sit for up to 72 hours before requiring cranking/priming the bowl. After that it does take a few seconds of cranking. If it was a daily driver, it would fire right up every time. So that tells me there is something up with your system. I would try to find and fix that before adding a pusher pump.